Cytochrome b gene structure and consequences for resistance to Qo inhibitor fungicides in plant pathogens

Abstract

The cytochrome b (cyt b) gene structure was characterized for different agronomically important plant pathogens, such as Puccinia recondita f sp tritici (Erikss) CO Johnston, P graminis f sp tritici Erikss and Hennings, P striiformis f sp tritici Erikss, P coronata f sp avenae P Syd & Syd, P hordei GH Otth, P recondita f sp secalis Roberge, P sorghi Schwein, P horiana Henn, Uromyces appendiculatus (Pers) Unger, Phakopsora pachyrhizi Syd & P Syd, Hemileia vastatrix Berk & Broome, Alternaria solani Sorauer, A alternata (Fr) Keissl and Plasmopara viticola (Berk & Curt) Berlese & de Toni. The sequenced fragment included the two hot spot regions in which mutations conferring resistance to QoI fungicides may occur. The cyt b gene structure of these pathogens was compared with that of other species from public databases, including the strobilurin-producing fungus Mycena galopoda (Pers) P Kumm, Saccharomyces cerevisiae Meyer ex Hansen, Venturia inaequalis (Cooke) Winter and Mycosphaerella fijiensis Morelet. In all rust species, as well as in A solani, resistance to QoI fungicides caused by the mutation G143A has never been reported. A type I intron was observed directly after the codon for glycine at position 143 in these species. This intron was absent in pathogens such as A alternata, Blumeria graminis (DC) Speer, Pyricularia grisea Sacc, Mycosphaerella graminicola (Fuckel) J Schröt, M fijiensis, V inaequalis and P viticola, in which resistance to QoI fungicides has occurred and the glycine is replaced by alanine at position 143 in the resistant genotype. The present authors predict that a nucleotide substitution in codon 143 would prevent splicing of the intron, leading to a deficient cytochrome b, which is lethal. As a consequence, the evolution of resistance to QoI fungicides based on G143A is not likely to evolve in pathogens carrying an intron directly after this codon.

Frequency of fungicide-resistant Botrytis cinerea populations isolated from ‘Thompson Seedless’ table grapes in the Central Valley of Chile

“…None of the Azo R isolates tested carried the Bcbi-143/144 intron; the presence of this intron in the cyt b gene prevents the occurrence of G143A-mediated resistance (Grasso et al, 2006;Yin et al, 2012) . Among the anilinopyrimidine fungicides, cyprodinil was used for a limited number of seasons for gray mold control in table grapes in Chile, until resistant populations emerged.…”

Emergence and early evolution of fungicide resistance in North American populations of Zymoseptoria tritici

“…The G143A substitution in the mitochondrial-encoded cytb protein explains the majority of QoI resistance (Grasso et al, 2006). A global survey of 841 Rhynchosporium secalis isolates sampled before the deployment of Qol fungicides showed that the G143A substitution was not detectable (Torriani et al, 2009b).…”

Phylogenetic diversity and sensitivity to MBI and QoI fungicides of <i>Magnaporthe oryzae</i> in Taiwan

“…Previous studies indicated that alternative oxidase (AOX) is one way to decrease the damage of strobilurin fungicides in certain fungal pathogens. 33,41,42) Furthermore, the culture medium added with an AOX inhibitor of salicylhydroxamic acid (SHAM) or n-propyl gallate (PG) could increase the inhibitory activity of strobilurins against fungal pathogens. 33,41,42) In this study, the M. oryzae isolates showed variable sensitivity to azoxystrobin and kresoxim-methyl, and the different sensitivities might be caused by the level of AOX activity in each M. oryzae isolate.…”

“…33,34) The mutation at codon 129 (TTC→ TTA) is associated with moderate resistance, and mutation at codon 143 (GGT→ GCT) is associated with resistance. 34) In Taiwan, rice blast is endemic to the first rice cultivation (March to June), affecting over 20,000 ha each year.…”